Thinking is a production of signs. If for a long time the subject has been held for the sole productor of these signs, it is now admitted that the subject itself, Ego and all, is the symbolic product of thinking. And if the human brain produces signs, what we have called spirit or unified consciousness are a modality of the materially existing physical body.
The vocabulary C.S. Peirce has given us accounts for the functionning of thinking. By relationing the sign triad of icon, index and symbol to the binary opposition between existence and essence, we are led to consider the different roles of iconicity. According to the mind’s intention to restrain the meaning of each sign to one valid signification or to disseminate the meaning by instauration, the icon will be logical or analogical.
The logical icon is used as a ground, a sort of idea to which the sign refers (1.551; 2.228), for the production of a sign of essence (e.g. a common noun, 2.260), while what we call the analogical icon is used as a ground for the production of a sign of existence (e.g. a colour seen by inner vision).
What goes for signs in general is also valid for mental signs. When thinking performs symbolization, the production of mental signs is submitted to the law of reductive or logical iconicity; when thinking performs indexicalization, it is submitted to the law of instaurative or analogical iconicity.
The neurophysiological description of mental activity in the human brain has clearly identified some of each hemisphere’s specific functions. The left hemisphere is specialized in language, reazoning, logic and analytical coding; the right hemisphere is specialized in the holistic perception of sets and the managment of body in space relations, it is also able to create visual and auditive patterns.
A concept is a set of signs with an apodictic (demonstrative) function produced mainly by the left hemisphere of the brain or under its supervision. An image is a set of signs with an apophantic (illustrative) function produced by the right hepmisphere.
The experiments of R.S.Sperry, J.E. Bogen, J. Eccles, D. Kimura, P.J.Vogel and M.S. Gazzaniga, to name but a few, allowed us to distinguish intra-hemispherical relations and inter-hemispherical relations in the human brain. Each hemisphere performs internal (ipsilateral) activity that the other hemisphere is not aware of and external activity involving the other hemisphere with which it then exchanges signs.